Radiation basics

Radiation is everywhere; living on this planet means being exposed to natural radiation. Artificial radiation has been used successfully in the last centuries for medical diagnosis and treatment of pathologies like cancer. The IAEA provides support to Member States to achieve safe and effective patient diagnosis and treatment using radiation.

Not only the cosmos and our environment contain radioactivity. Even the elements our bodies are made of are naturally found in different variants – isotopes – some of which are radioactive, for example the radioisotopes of potassium, caesium and radium.

Similar to visible light, radiation is of electromagnetic nature. When it is powerful enough to break molecular bonds, thereby ionizing matter (the process during which a neutral atom or molecule loses or gains electrons to form ions), it is called ‘ionizing radiation.’ Molecular bonds may occur in all materials, even in the building blocks of life – the DNA.

There is evidence that shows that alterations to DNA molecules caused by ionizing radiation may generate mutated biological cells. The vast majority of these mutations are not dangerous to human health, but there is a small probability that some mutations may cause cancer. For this reason, it is vital to understand how radiation interacts with biological matter.

Ionizing radiation can penetrate solid objects deeply. This characteristic is the basis for diagnostic radiology and radiotherapy. X rays, one of the forms of ionizing radiation, are emitted from an irradiation device on one side of the object. The radiation that passes through the object is detected by suitable detectors on the other side. This process can be used to produce an image that shows the internal structures of the irradiated object without opening it. When this process is applied in medicine, in a specialised field called diagnostic radiology, it provides images of the internal structures of the human body with minimal intervention.

In nuclear medicine, medical practitioners inject patients with a radioactive substance that accumulates in a targeted part of the body. By detecting the radiation exiting the body they can draw conclusions about the physiological functions of the anatomy. In radiotherapy, radiation penetrates the body to target and destroy tumours.

Natural sources make up around 80 per cent of the global average annual dose people are exposed to. The largest artificial source of exposure for humans is medical radiation. Its contribution to the total average annual dose is around 20 per cent. This is about half of the contribution of the largest natural component – radon inhalation in buildings – to the average annual dose.

For this reason, it is important to minimize unwarranted medical exposures to ionizing radiation. This is achieved by improving the processes of justification and optimization of exposures. Justification requires that a person may be exposed to radiation only when there is a clear net benefit for him or her. Optimization processes on the other hand minimize the radiation dose used to achieve a specific diagnostic or therapeutic result to the lowest level that is achievable and reasonable.